Almost every motorist has experienced the inconvenience of a car that will not start due to the primary battery being discharged to the point that the car's electric starting motor will not function. Usually the headlights have been left burning inadvertently or the charging system has failed.
Traditionally, recourse has been made to one of several techniques for restarting a stranded car with a discharged battery. The "push" start, where the vehicle is pushed to a slow rolling velocity and then the clutch suddenly engaged to turn the engine requires physical strength or another vehicle to provide the push, and sufficient clear space ahead of the vehicle to complete the operation. "Push" starts are not feasible in most cases for vehicles with an automatic transmission. Another technique involves a jumper cable to provide power to the discharged battery from the battery posts of a car which is not discharged. The use of a jumper cable is hazardous due to the fact that if the polarities of the two ends of the jumper cables are reversed, a serious short circuit results and great damage and possibly an explosion can result. Other types of "jumper" cables which plug into the cigar lighters of the two cars are safer, but due to the small wire used, are relatively ineffective to accomplish the desired recharge necessary to start the stalled car.
Recently, packs of rechargeable nickel-cadmium batteries have been available as a portable and independent charging device. While under the best conditions, such a rechargeable reserve battery accomplishes the desired objective, it suffers from at least one serious defect in that it must be recharged regularly due to a high rate of self-discharge in storage, especially in hot weather, when stored in the average car trunk or glove box. Ordinary flashlight batteries have also been used in battery packs provided to start stalled cars, which are even more prone to deterioration during storage.